A few years ago, Linda Alterwitz noticed her husband watching something interesting on TV. An artist and photographer, she’d previously worked with X-rays, MRIs and other medical techniques to reveal visualizations invisible to the unaided eye, and she saw an intriguing image on the screen during an episode of Cops.

“The helicopter was chasing a person running, in the pitch-black night, and this thermal camera showed amazing silhouetted images,” she says. “I saw it, and my first thought was ‘how can I get one of those cameras?’”

When she looked into the idea, she found that professional-quality thermographic cameras—used most often for military, police and medical purposes—cost tens of thousands of dollars. But when she got in touch with a company in her hometown of Las Vegas called Sierra Pacific Innovations that made these types of cameras, they were willing to lend her one for artistic purposes.

In the years since, as part of her “Thermal” project, Alterwitz has used thermal cameras to photograph family, friends, strangers and even dogs in both black-and-white and color. “Essentially, it’s a camera with a sensor that detects heat radiation, instead of light,” she says. “The neatest thing about it is the experimentation process, because you never know what effects you’re going to produce.”

At times, she’s gone out into crowded public places to shoot portraits of strangers, not always clueing them in on the technology she’s using. ”The thermal cameras look like old movie cameras—big and bulky, and you hold them on your shoulder,” she says. “Which is really great for me, because a lot of people don’t really know what I’m doing with it, they think I’m taking movies.”

For her “Core” series, shot at home, Alterwitz’ subjects lifted up their shirts or otherwise exposed their bodies so that the camera could pick up unexpected thermal signatures of their blood vessels. “My son was in the hot tub, and he came out, and it basically looked like his circulatory system was on fire,” she says, describing the image at top. “It looks like tree branches climbing up his body.”

Alterwitz initially decided to shoot the “Canine” series because her dog Ruby “is a really good model, and always available.” When she shot the image above, “Ruby had just finished drinking and she had water spots all over her face which were only made visible through the lens of the thermal camera,” she explains. “So what we’re seeing are cold spots of water on her face in relation to her warm body temperature.”

When she shot a friend’s dog with its head resting out of a car window, above, Alterwitz discovered that heat radiation is entirely blocked by glass—so the image shows a red-hot dog cut off by a cool glass window.

Once, Alterwitz was inspired to use the camera to take a self-portrait. “I’d gotten a facial, and my face was all swollen and enflamed, and I had the camera with me,” she says. “So I asked my husband to take a photo of all the heat and inflammation coming off it.”

She’s constantly looking for hidden thermal images she can capture with the cameras—next, she wants to take photos of people getting tattoos, which she hopes will reveal tiny dots of inflammation where the needle punctures their skin.

“After a while, I realized it’s really a different way of seeing the world. We’re used to seeing in terms of light, but that’s just one way of portrating visual information,” Alterwitz says. “My brain gets totally focused on heat, and cold—at times, I’ve even dreamed in thermal.”

Like this article?SIGN UP for our newsletter

About Joseph Stromberg

Joseph Stromberg is a science reporter for Vox.com. He was previously a digital reporter for Smithsonian.